Methods of forming a bulk field effect transistor (FET) with sub-source/drain isolation layers and the resulting structures

ABSTRACT

Disclosed are structures (e.g., a fin-type field effect transistor (FINFET) and a nanowire-type FET (NWFET)) and methods of forming the structures. In the methods, a fin is formed. For a FINFET, the fin includes a first semiconductor material. For an NWFET, the fin includes alternating layers of first and second semiconductor materials. A gate is formed on the fin. Recesses are formed in the fin adjacent to the gate and extend to (or into) a semiconductor layer, below, made of the second semiconductor material. An oxidation process forms oxide layers on exposed semiconductor surfaces in the recesses including a first oxide material on the first semiconductor material and a second oxide material on the second semiconductor material. The first oxide material is then selectively removed and source/drain regions are formed by lateral epitaxial deposition in the recesses. The remaining second oxide material minimizes sub-channel region source-to-drain leakage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims the benefit under 35 U.S.C. § 120 as adivisional of U.S. patent application Ser. No. 15/632,922 filed on Jun.26, 2017, now issued as U.S. Pat. No. 10,134,901 on Nov. 20, 2018, theentire teachings of which are incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to bulk non-planar field effecttransistors (FETs), such as bulk fin-type FETs or bulk stackednanowire-type FETs, and methods of forming such FETs to minimizethrough-substrate source-to-drain leakage.

Description of Related Art

Integrated circuit (IC) design decisions are often driven by devicescalability, device density, manufacturing efficiency and costs. Forexample, size scaling of planar field effect transistors (FETs) resultedin the development of planar FETs with relatively short channel lengthsand, consequently, the smaller channel lengths resulted in acorresponding increase in short channel effects.

In response, fin-type FETs (FINFETs) were developed. A FINFET is anon-planar FET that incorporates a semiconductor fin (i.e., a relativelytall and thin, elongated, rectangular-shaped, semiconductor body) and,within the semiconductor fin, a channel region positioned laterallybetween source/drain regions. A gate structure is positioned adjacent tothe top surface and opposing sidewalls of the semiconductor fin at thechannel region. Such a FINFET exhibits two-dimensional field effects ascompared to the single-dimensional field effects exhibited by a planarFET and, thus, exhibits improved gate control over the channel. Itshould be noted that, because the semiconductor fin is so thin, anyfield effects exhibited at the top surface are insignificant (i.e.,negligible).

Recently, to improve drive current and allow for further device sizescaling, nanowire-type FETs (NWFETs), including both horizontal NWFETsand vertical NWFETs, have been developed. For example, a horizontalNWFET, like a FINFET, is a non-planar FET that is formed using asemiconductor fin above a substrate. However, in this case, a portion ofthe semiconductor fin, which is positioned laterally between thesource/drain regions, is processed to form one or more nanowires, whichare oriented horizontally (e.g., parallel to the top surface of thesubstrate and which extends between the source/drain regions. In thecase of multiple nanowires, they can be physically separated from eachother and stacked one above the other. The nanowire(s) function as achannel region(s) and is/are physically separated from the semiconductormaterial below. A gate structure is formed so that it wraps around thenanowire(s)/channel region(s). Such a NWFET exhibits multi-dimensionalfield effects as compared to the two dimensional field effects exhibitedby FINFET and, thus, exhibits improved gate control over the channelregion(s).

The above-described FINFETs and NWFETs can be formed assemiconductor-on-insulator structures. Alternatively, such FETs can beformed as bulk structures. In the case of bulk structures, ground planedoping in the form of a well region is used in the bulk semiconductorsubstrate below the device to prevent through-substrate source-to-drainleakage, which can negatively impact device on-off characteristics.Specifically, doped well regions in a bulk semiconductor substrate belowthe device to prevent direct current flow from the source region to thedrain region by creating diode junctions between the source region andground plane and between the drain region and the ground plane.Unfortunately, as device sizes continue to be scaled, ground planedoping in the bulk semiconductor substrate may not be sufficient forpreventing such through-substrate source-to-drain leakage in FINFETs orin NWFETs.

SUMMARY

In view of the foregoing, disclosed herein disclosed herein are methodsof forming a semiconductor structure that includes a non-planar fieldeffect transistor (FET), such as fin-type FET (FINFET) or nanowire FET(NWFET). In the methods, a semiconductor fin can be formed. For aFINFET, the semiconductor fin can be a first semiconductor material. Foran NWFET, the semiconductor fin can include alternating layers of afirst semiconductor material and a second semiconductor material. A gatestructure can be formed on the semiconductor fin. Then, recesses can beformed in the semiconductor fin on either side of the gate structure andcan extend vertically to (or into) a semiconductor layer, which is belowthe fin and made of the second semiconductor material. An oxidationprocess can then be performed to form oxide layers on exposedsemiconductor surfaces. Oxide layers on the first semiconductor materialwill be a first oxide material and those on the second semiconductormaterial will be a second oxide material. The first oxide material canbe selectively removed and source/drain regions can be formed by lateralepitaxial deposition in the recesses. Also disclose herein areembodiments of a semiconductor structure that includes a non-planar FETstructure (e.g., a FINFET or NWFET) form according to the above-describemethod so as to have local isolation layers (i.e., the remaining oxidelayers), which are below the source/drain regions and which minimize andpreferably prevent through-substrate and, particularly, sub-channelregion source-to-drain leakage (i.e., source-to-drain leakage below thechannel region).

More particularly, disclosed herein is a method of forming asemiconductor structure that includes a fin-type FET (FINFET). In themethod, a semiconductor fin, which is made of a first semiconductormaterial (e.g., silicon), can be formed on semiconductor layer, which ismade of a second semiconductor material (e.g., silicon germanium) thatis different from the first semiconductor material and which is above abulk semiconductor substrate. The semiconductor fin can have a firstportion that is positioned laterally between second portions. Asacrificial gate structure can be formed adjacent to the first portionof the semiconductor fin such that the second portions extend laterallybeyond the gate structure. A dielectric layer can subsequently be formedon the semiconductor layer such that it is positioned laterally adjacentto sidewalls of the semiconductor fin and, particularly, immediatelyadjacent to the exposed sidewalls of the second portions of thesemiconductor fin. Then, recesses can be formed through the secondportions to (or into) the semiconductor layer below.

After the recesses are formed, an oxidation process can be performed inorder to form oxide layers on exposed semiconductor surfaces within therecesses (i.e., on exposed semiconductor surfaces of the semiconductorlayer at the bottoms of the recesses and exposed semiconductor surfacesof the semiconductor fin on the inner sides of the recesses closest tothe gate structure). Since the semiconductor fin is made of the firstsemiconductor material and the semiconductor layer is made of the secondsemiconductor material, the oxide material on these components willvary. Specifically, the oxidation process will result in a first oxidematerial (e.g., silicon dioxide) being formed on the first semiconductormaterial and a second oxide material (e.g., silicon germanium oxide)that is different from the first oxide material being formed on thesecond semiconductor material. Next, the first oxide material can beselectively removed, leaving oxide layers, which are made of the secondoxide material and which are in the bottoms of the recesses, intact.Then, source/drain regions can be formed in the recesses (e.g., bylateral epitaxial deposition on the exposed vertical surfaces of thesemiconductor fin within the recesses). The second oxide material, whichremains intact at the bottoms of the recesses, will electrically isolateand physically separate the source/drain regions from the semiconductorlayer below.

Additional processing can be performed to complete the FINFET structure.This additional processing can include, but is not limited to, removingthe sacrificial gate structure and replacing it with a replacement metalgate.

Also disclosed herein is a method of forming a semiconductor structurethat includes a nanowire FET (NWFET). In the method, a multi-layersemiconductor fin can be formed on semiconductor layer above a bulksemiconductor substrate. The bulk semiconductor substrate can be made ofa first semiconductor material, the semiconductor layer can be a secondsemiconductor material that is different from the first semiconductormaterial and the multi-layer semiconductor fin can include alternatinglayers of the first semiconductor material and the second semiconductormaterial. The multi-layer semiconductor fin can have a first portionthat is positioned laterally between second portions. A sacrificial gatestructure can then be formed adjacent to the first portion of thesemiconductor fin such that the second portions extend laterally beyondthe gate structure. A dielectric layer can subsequently be formed on thesemiconductor layer such that it is positioned laterally adjacent tosidewalls of the semiconductor fin and, particularly, immediatelyadjacent to the exposed sidewalls of the second portions of thesemiconductor fin. Then, recesses can be formed through the secondportions to (or into) the semiconductor layer below.

After the recesses are formed, an oxidation process can be performed inorder to form oxide layers on exposed semiconductor surfaces within therecesses (i.e., on exposed semiconductor surfaces of the semiconductorlayer at the bottoms of the recesses and exposed semiconductor surfacesof the semiconductor fin on the inner sides of the recesses closest tothe gate structure). Since the semiconductor fin is made of alternatinglayers of the first and second semiconductor materials and thesemiconductor layer is made of the second semiconductor material, theoxide material on these components will vary. Specifically, theoxidation process will result in a first oxide material (e.g., silicondioxide) being formed on the first semiconductor material of thealternating layers in the semiconductor fin and a second oxide material(e.g., silicon germanium oxide) that is different from the first oxidematerial being formed on the second semiconductor material of thealternating layers of the semiconductor fin and of the semiconductorlayer. Next, the first oxide material can be selectively removed,leaving oxide layers, which are made of the second oxide material andwhich are in the bottoms of the recesses and on the vertical surfaces ofevery other layer in the semiconductor fin, intact. Subsequently,source/drain regions can be formed in the recesses (e.g., by lateralepitaxial deposition on any exposed vertical surfaces of thesemiconductor fin within the recesses). The second oxide material, whichremains intact at the bottoms of the recesses, will electrically isolateand physically separate the source/drain regions from the semiconductorlayer below.

Additional processing can be performed to complete the NWFET structure.This additional processing can include, but is not limited to,selectively removing the sacrificial gate structure to expose the firstportion of the semiconductor fin; selectively removing each exposedlayer of the second semiconductor material from the first portion suchthat at least one nanowire of the first semiconductor material remains;and forming replacement gate structure wrapping around the at least onenanowire.

Also disclosed herein are semiconductor structures formed according tothe above-described methods. Each semiconductor structure can include abulk semiconductor substrate, a semiconductor layer on the bulksemiconductor substrate and a non-planar field effect transistor (FET)on the semiconductor layer. The non-planar FET can be, for example, afin-type FET (FINFET) or a nanowire FET (NWFET). In either case, the FETcan include source/drain regions, at least one channel region positionedlaterally between the source/drain regions and a gate structure adjacentto the channel region(s). The channel region (or regions) can be a firstsemiconductor material (e.g., silicon) and the semiconductor layer canbe a second semiconductor material that is different from the firstsemiconductor material (e.g., silicon germanium). Additionally, eachsemiconductor structure can include layers of oxide material thatelectrically isolate and physically separate the source/drain regionsfrom the semiconductor layer below. Thus, these layers of oxide materialfunction as local isolation layers that minimize and preferably preventthrough-substrate and, particularly, sub-channel region source-to-drainleakage (i.e., source-to-drain leakage below the channel region).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention will be better understood from the followingdetailed description with reference to the drawings, which are notnecessarily drawn to scale and in which:

FIG. 1 is a flow diagram illustrating a method of forming asemiconductor structure that includes a fin-type field effect transistor(FINFET);

FIG. 2 is a cross-section diagram illustrating a partially completedstructure formed according to the flow diagram of FIG. 1;

FIGS. 3A-3B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 1;

FIGS. 4A-4B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 1;

FIGS. 5A-5B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 1;

FIGS. 6A-6C are different cross-section diagrams illustrating apartially completed structure formed at process 312 of the flow diagramof FIG. 1;

FIGS. 7A-7C are different cross-section diagrams illustrating analternative partially completed structure formed at process 312 of theflow diagram of FIG. 1;

FIGS. 8A-8C are different cross-section diagrams illustrating apartially completed structure formed at process 314 of the flow diagramof FIG. 1 using the partially completed structure of FIGS. 6A-6C;

FIGS. 9A-9C are different cross-section diagrams illustrating analternative partially completed structure formed at process 314 of theflow diagram of FIG. 1 using the partially completed structure shown inFIGS. 7A-7C;

FIGS. 10A-10C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 1;

FIGS. 11A-11C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 1;

FIGS. 12A-12C are different cross-section diagrams illustrating asemiconductor structure that is formed according to the method of FIG. 1and that includes a FINFET;

FIG. 13 is a flow diagram illustrating a method of forming asemiconductor structure that includes a nanowire-type field effecttransistor (NWFET);

FIG. 14 is a cross-section diagram illustrating a partially completedstructure formed according to the flow diagram of FIG. 13;

FIGS. 15A-15B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 16A-16B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 17A-7B are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 18A-18C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 19A-19C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13 and, particularly, an alternative structure as compared to thatshown in FIGS. 18A-18C;

FIGS. 20A-20C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 21A-21C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13 and, particularly, an alternative structure as compared to thatshown in FIGS. 20A-20C;

FIGS. 22A-22C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 23A-23C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 24A-24C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 25A-25C are different cross-section diagrams illustrating apartially completed structure formed according to the flow diagram ofFIG. 13;

FIGS. 26A-26C are different cross-section diagrams illustrating apartially completed structure formed at process 324 of the flow diagramof FIG. 13; and

FIGS. 27A-27C are different cross-section diagrams illustrating analternative partially completed structure formed at process 324 of theflow diagram of FIG. 13;

FIGS. 28A-28C are different cross-section diagrams illustrating asemiconductor structure that is formed according to the flow diagram ofFIG. 13 using the partially completed structure of FIGS. 26A-26C andthat includes a NWFET 400; and

FIGS. 29A-29C are different cross-section diagrams illustrating asemiconductor structure that is formed according to the flow diagram ofFIG. 13 using the partially completed structure of FIGS. 27A-27C andthat includes a NWFET 400′.

DETAILED DESCRIPTION

As mentioned above, when non-planar field effect transistors (FETs),such as fin-type FETs (FINFETs) and nanowire FETs (NWFETs) are formed asbulk semiconductor structures, the ground plane doping in the bulksemiconductor substrate may not be sufficient for preventingthrough-substrate and, particularly, sub-channel region source-to-drainleakage (i.e., source-to-drain leakage below the channel region portionof the fin).

In view of the foregoing, disclosed herein are methods of forming asemiconductor structure that includes a non-planar field effecttransistor (FET), such as fin-type FET (FINFET) or nanowire FET (NWFET).In the methods, a semiconductor fin can be formed. For a FINFET, thesemiconductor fin can be a first semiconductor material. For an NWFET,the semiconductor fin can include alternating layers of a firstsemiconductor material and a second semiconductor material. A gatestructure can be formed on the semiconductor fin. Then, recesses can beformed in the semiconductor fin on either side of the gate structure andcan extend vertically to (or into) a semiconductor layer, which is belowthe fin and made of the second semiconductor material. An oxidationprocess can then be performed to form oxide layers on exposedsemiconductor surfaces. Oxide layers on the first semiconductor materialwill be a first oxide material and those on the second semiconductormaterial will be a second oxide material. The first oxide material canbe selectively removed and source/drain regions can be formed by lateralepitaxial deposition in the recesses. Also disclose herein areembodiments of a semiconductor structure that includes a non-planar FETstructure (e.g., a FINFET or NWFET) form according to the above-describemethod so as to have local isolation layers (i.e., the remaining oxidelayers), which are below the source/drain regions and which minimize andpreferably prevent through-substrate and, particularly, sub-channelregion source-to-drain leakage (i.e., source-to-drain leakage below thechannel region).

More particularly, FIG. 1 is a flow diagram illustrating a method offorming a semiconductor structure that includes a fin-type FET (FINFET).The method begins with a bulk semiconductor substrate 201 or wafer (seeprocess 102 and FIG. 2). This bulk semiconductor substrate 201 can, forexample, be made of a first semiconductor material (e.g., silicon).

A semiconductor layer 202 can be formed on a top surface of thesemiconductor substrate 201 and an additional semiconductor layer 203can be formed on a top surface of the semiconductor layer 202 (seeprocess 104 and FIG. 2). The semiconductor layer 202 can be made of asecond semiconductor material (e.g., silicon germanium), which isdifferent from the first semiconductor material. This semiconductorlayer 202 can be formed, for example, by epitaxial deposition or anyother suitable deposition technique. Optionally, this semiconductorlayer 202 can be in-situ doped (or subsequently implanted) so as to havea first-type conductivity at a relatively high conductivity level. Theadditional semiconductor layer 203 can subsequently be formed on thesemiconductor layer 202. This additional semiconductor layer 203 can bemade of the first semiconductor material (e.g., silicon) and cansimilarly be formed by epitaxial deposition or any other suitabledeposition technique.

A semiconductor fin 210 can be formed from the additional semiconductorlayer 203 above the semiconductor layer 202 (see process 106 and FIGS.3A-3B). Techniques for forming a semiconductor fin including, but notlimited to, conventional lithographic patterning and etch techniques andsidewall image transfer (SIT) techniques, are well known in the art.Thus, the details of such techniques have been omitted from thisspecification in order to allow the reader to focus on the salientaspects of the disclosed methods. During subsequent processing, achannel region for the FINFET will be formed using a first portion 211(e.g., a center portion) of the semiconductor fin 210 and source/drainregions for the FINFET will be formed using second portions 212 (e.g.,end portions) on opposing sides of the first portion 211. Since theadditional semiconductor layer 203 is made of the first semiconductormaterial (e.g., silicon), so is the resulting semiconductor fin 210.

For purposes of this disclosure, a semiconductor fin refers to arelatively thin, tall, elongated semiconductor body. The semiconductorfin can be formed (e.g., patterned) so as to be essentially rectangularin shape. That is, the semiconductor fin can have an essentially uniformwidth and height across the length of the semiconductor fin (e.g., inthe first portion 211 and the second portions 212). Alternatively, thesemiconductor fin could be formed (e.g., patterned) so as to have afirst width in the first portion 211 and a second width, which isgreater than the first width, in the second portions 212.

Optionally, the semiconductor fin 210 can be doped (e.g., prior topatterning or after patterning) so as to have the first-typeconductivity at a relatively low conductivity level and, thus, such thatthe channel region of the FINFET being formed will have this sameconductivity. Alternatively, the semiconductor fin 210 can remainundoped such that the channel region of the FINFET being formed willalso be undoped.

A sacrificial gate structure 220, having a sacrificial gate cap 221 anda gate sidewall spacer 222, can be formed adjacent to the opposing sidesand top surface of the first portion 211 of the semiconductor fin 210(see process 108 and FIGS. 4A-4B). This sacrificial gate structure 220will function as a placeholder for subsequent replacement metal gate(RMG) processing (discussed in greater detail below at process 120).More specifically, a sacrificial gate stack can be formed over thesemiconductor fin. In one exemplary embodiment, the sacrificial gatestack can include multiple dielectric layers including at least ablanket dielectric layer and a dielectric cap layer on the blanketdielectric layer. For example, the blanket dielectric layer can bedeposited onto the partially completed structure (e.g., over thesemiconductor layer 202 and the semiconductor fin 210) and polished(e.g., using a chemical mechanical polishing (CMP) process) such that ithas a thickness that is greater than the height of the semiconductor fin210 (i.e., such that the top surface of the blanket dielectric layer isabove the level of the top surface of the semiconductor fin 210). Thisblanket dielectric layer can be, for example, a blanket layer of siliconnitride, silicon oxycarbide, silicon carbon nitride, silicon boroncarbon, or some other dielectric material that can be selectively etchaway from the semiconductor fin 210 and semiconductor layer 202 atprocess 120 below. The dielectric cap layer can be deposited onto theblanket dielectric layer. The dielectric cap layer can be, for example,a thin layer of silicon nitride or some other suitable dielectricmaterial. Lithographic patterning and etch processes can then beperformed in order to form, from this sacrificial gate stack, asacrificial gate structure 220 having a sacrificial gate cap 221 (asillustrated). A gate sidewall spacer 222 can further be formed on thesidewalls of the sacrificial gate structure 220, as illustrated in FIGS.4A-4B. To form the gate sidewall spacer 222, a relatively thin conformaldielectric spacer layer can be deposited over the partially completedstructure. An anisotropic etch process can then be performed so as toremove the conformal dielectric spacer layer from horizontal surfaces,thereby forming the gate sidewall spacer 222 on the essentially verticalsurfaces of the sacrificial gate structure 220. It should be noted thatthe dielectric material of the dielectric spacer layer should be adifferent dielectric material than that used for the sacrificial gatestructure 220 so that when the sacrificial gate structure 220 isselectively etch away from the semiconductor fin 210 and semiconductorlayer 202 at process 120 below, the gate sidewall spacer 222 remainsintact. For example, if the sacrificial gate structure 220 is a siliconnitride structure, then the dielectric spacer layer used for the gatesidewall spacer 222 could be a relatively thin conformal siliconoxycarbide spacer layer.

At least one interlayer dielectric (ILD) layer 230 can subsequently beformed on the semiconductor layer 202 (see process 110 and FIGS. 5A-5B).For example, a blanket layer of ILD material can subsequently bedeposited onto the semiconductor layer 202, over the semiconductor fin210, over the gate sidewall spacer 222 and further over the sacrificialgate cap 221 on the sacrificial gate structure 220. This blanket layerof ILD material can be polished (e.g., using a CMP process) and thenrecessed to expose the top surfaces of the second portions 212 of thesemiconductor fin 210. Thus, the resulting ILD layer 230 will bepositioned laterally adjacent to sidewalls of the semiconductor fin 210and, particularly, adjacent to the sidewalls of the second portions 212of the semiconductor fin 210. The ILD material of this ILD layer 230should be different from the dielectric materials used for the gatesidewall spacer 222 and for the sacrificial gate structure 220 to allowfor recessing the ILD layer 230 without recessing the gate sidewallspacer 222. For example, the ILD material can be silicon dioxide or someother suitable ILD material (e.g., borophosphosilicate glass (BPSG),tetraethyl orthosilicate (TEOS), fluorinated tetraethyl orthosilicate(FTEOS), etc.).

Recesses 232 can then be formed such that they extend completely throughthe second portions 212 of the semiconductor fin 210 to the top surfaceof the semiconductor layer 202 below or, alternatively, completelythrough the second portions 212 of the semiconductor fin 210 and furtherpartially into the semiconductor layer 202 below (see process 112).Specifically, to form the recesses 232, an anisotropic etch process thatis selective for the semiconductor material of the semiconductor fin 210over the adjacent dielectric materials (e.g., over dielectric materialsof the ILD layer 230, the gate sidewall spacer 222 and the sacrificialgate cap 221) can be performed. This etch process can stop at the topsurface of the semiconductor layer 202, as shown in FIGS. 6A-6C.Alternatively, this etch process can stop when the bottoms of therecesses 232 are some distance below the top surface of thesemiconductor layer 202, but still above the bottom surface of thesemiconductor layer 202 (see FIGS. 7A-7C).

After the recesses 232 are formed, an oxidation process can be performedin order to form oxide layers on exposed semiconductor surfaces withinthe recesses 232 (i.e., on exposed semiconductor surfaces of thesemiconductor layer 202 at the bottoms of the recesses 232 and exposedsemiconductor surfaces of the semiconductor fin 210 on the inner sidesof the recesses closest to the sacrificial gate structure 220) (seeprocess 114 and FIGS. 8A-8C or FIGS. 9A-9B). Since the semiconductor finis made of the first semiconductor material and the semiconductor layer202 is made of the second semiconductor material, the oxide material onthese components will vary. Specifically, the oxidation process willresult in layers of a first oxide material 241 (e.g., silicon dioxide)being formed on the exposed first semiconductor material surfaces of thesemiconductor fin 210 at the inner sides of the recesses 232 and layersof a second oxide material 242 (e.g., silicon germanium oxide), which isdifferent from the first oxide material 241, being formed on the exposedsecond semiconductor material surfaces of the semiconductor layer 202 atthe bottom of the recesses. It should be noted that if the recesses 232only extend to the top surface of the semiconductor layer 202, as shownin FIGS. 6A-6C, without further extending into the semiconductor layer202, then the second oxide material 242 will be formed on the topsurface only of the semiconductor layer 202 (as shown in FIGS. 8A-8C).However, if the recesses 232 extend partially into the semiconductorlayer 202 (as shown in FIGS. 7A-7C), then the second oxide material willbe formed at process 114 on vertical and horizontal surfaces of thesemiconductor layer 202 within lower portions of the recesses 232 (asshown in FIGS. 9A-9C).

For illustration purposes, the remaining processes of the flow diagramof FIG. 1 are illustrated in the drawings with respect to the partiallycompleted structure shown in FIGS. 9A-9C. However, it should beunderstood that the drawings are not intended to be limiting and that,alternatively, these same processes could, alternatively, be performedwith respect to the partially completed structure shown in FIGS. 8A-8C.

Next, the first oxide material 241 can be selectively removed, leavingoxide layers, which are made of the second oxide material 242 and whichare in the bottoms of the recesses 232, intact (see process 116 andFIGS. 10A-10C). For example, a selective isotropic etch process can beperformed in order to selectively remove the first oxide material 241(e.g., silicon dioxide) from the semiconductor fin 210 on the innersides of the recesses 232 closest to the sacrificial gate structure 220such that the second oxide material 242 remains essentially intact. Oneexemplary selective isotropic etch process that could be used at process116 to selectively etch silicon dioxide over silicon germanium oxide(i.e., to etch silicon dioxide at a significantly faster rate thansilicon germanium oxide) is a remote plasma-based ammonium fluoride(NH4F) etch process, such as a SiConi™ process. Alternatively, any othersuitable isotropic etch process which etches silicon dioxide at asignificantly faster rate than silicon germanium oxide could be used. Itshould be noted that if the ILD layer 230 is a silicon dioxide layer,then this layer will also be etched back to some degree at process 116(not shown).

Following removal of the first oxide material 241 at process 116,source/drain regions 213 can be formed in the recesses 232 and thesecond oxide material 242, which remains intact at the bottoms of therecesses 232, will electrically isolate and physically separate thesource/drain regions 213 from the semiconductor layer 202 below (seeprocess 118 and FIGS. 11A-11C). For example, the source/drain regions213 can be formed by lateral epitaxial deposition of a thirdsemiconductor material on the exposed vertical surfaces of thesemiconductor fin 210 within the recesses 232 (i.e., on the inner sidesof the recesses 232 closest to the sacrificial gate structure 220). Thisthird semiconductor material of the source/drain regions 213 and thefirst semiconductor material of the remaining portion 211 (i.e., thechannel region) of the semiconductor fin 210 between the source/drainregions 213 can be the same material (e.g., silicon). Alternatively, thethird semiconductor material can be different from the firstsemiconductor material and can be preselected to enhance charge carriermobility, depending upon the conductivity-type of the FET being formed.For example, for a P-type FET, the third semiconductor material of thesource/drain regions 213 could be silicon germanium (SiGe), which willenhance hole mobility within the P-type FET's channel region and,thereby enhance performance. For an N-type FET, the third semiconductormaterial of the source/drain regions 213 could be silicon carbide (SiC),which will enhance electron mobility within the N-type FET's channelregion and, thereby enhance performance.

In any case, the source/drain regions 213 can be in-situ doped (orsubsequently implanted) so as to have a second-type conductivity at arelatively high level. This second-type conductivity can be differentfrom the first-type conductivity of the channel region 211 and thesemiconductor layer 202 below. Specifically, those skilled in the artwill recognize that, for a P-type FET, the first-type conductivity ofthe channel region 211 can be N-type conductivity and the second-typeconductivity of the source/drain regions 213 can be P-type conductivity.In this case, the semiconductor layer 202 below the source/drain regions213 can, optionally, also be doped so as to have the N-typeconductivity, thereby creating diode junctions to further provideprotection against any through-substrate and, particularly, sub-channelregion source-to-drain leakage (i.e., source-to-drain leakage below thechannel region portion of the fin). Contrarily, for an N-type FET, thefirst-type conductivity of the channel region 211 can be P-typeconductivity and the second-type conductivity of the source/drainregions 213 can be N-type conductivity. In this case, the semiconductorlayer 202 below the source/drain regions 213 can, optionally, also bedoped so as to have the P-type conductivity, thereby creating diodejunctions to further provide protection against any through-substrateand, particularly, sub-channel region source-to-drain leakage (i.e.,source-to-drain leakage below the channel region portion of the fin).

Additional processing can subsequently be performed in order to completethe FINFET structure 200 (see process 120 and FIGS. 12A-12C). Thisadditional processing can include, but is not limited to, the following:depositing at least one additional ILD layer 235 (e.g., made of the sameILD material as the ILD layer 230 or a different material); polishingthe additional ILD layer 235 such that a top surface of the sacrificialgate structure 220 is exposed; selectively removing the sacrificial gatestructure 220 to create a gate opening; replacing the sacrificial gatestructure 220 with a replacement metal gate (RMG) 225 having adielectric gate cap 226 (i.e., forming a RMG 225 with a dielectric gatecap 226 in the gate opening); performing middle of the line (MOL)process (e.g., forming contacts to the RMG 225 and the source/drainregions 213 (not shown)); and performing back end of the line (BEOL)processing.

In the above-described method, the following exemplary processes can beused to form the RMG 225. A gate dielectric layer can be conformallydeposited so that the exposed top surface and sidewalls of thesemiconductor fin 210 at the channel region 211 are covered. Thoseskilled in the art will recognize that, due to the conformal depositionprocess, the gate dielectric layer will also cover exposed horizontalsurfaces of the semiconductor layer 202 and vertical surfaces of thegate sidewall spacers 222 within the gate opening. The gate dielectriclayer can be, for example, high-K gate dielectric layer. Subsequently, awork function metal layer can be conformally deposited in the gateopening over the gate dielectric layer. The metal material or metalalloy material of the conformal work function metal layer can bepreselected in order to achieve the optimal gate conductor work functiongiven the conductivity type of the FINFET 200. The work function metallayer can then, optionally, be chamfered. The chamfering process caninclude: depositing a protective fill material onto the work functionmetal layer; recessing the protective fill material; etching away theexposed work function metal material from above the protective fillmaterial such that the maximum height of the work function metal layeris below the level of the top surface of the gate sidewall spacer; andremoving the protective fill material. A conductive fill material can bedeposited to fill any remaining space in the gate opening and apolishing process (e.g., a CMP process) can be performed to remove anyRMG materials from above the top surface of the additional ILD layer235. A dielectric gate cap 226 can then be formed on the top surfaces ofthe RMG 225. For example, the conductive fill material can be recessed(i.e., etched back) and a dielectric cap layer (e.g., a silicon nitridecap layer) can be deposited over the partially completed structure so asto fill the recess above the conductive fill material. Next, a polishingprocess (e.g., a CMP process) can be performed so as to remove any ofthe dielectric cap material from above the top surface of the additionalILD layer 235, thereby forming the dielectric gate cap 226. Sincevarious RMG structures and the methods of making them are well known inthe art and could be incorporated into the FET 200 being formed, onlythe RMG 225, as a whole, is illustrated in FIGS. 12A-12C. The individualcomponents of the RMG 225, including the gate dielectric layer, the workfunction metal layer, the fill metal, etc., are not specificallyillustrated in the figures in order to allow the reader to focus on thesalient aspects of the disclosed method.

Referring to the flow diagram of FIG. 13, also disclosed herein is amethod of forming a semiconductor structure that includes a nanowire FET(NWFET). The method begins with a bulk semiconductor substrate 401 orwafer (302). This bulk semiconductor substrate 401 can, for example, bemade of any suitable semiconductor material. For example, thesemiconductor substrate 401 can be made of a first semiconductormaterial (e.g., silicon) or some other suitable semiconductor material.

A semiconductor layer 402 can be formed on a top surface of thesemiconductor substrate 401 and a stack 403 of additional semiconductorlayers can be formed on a top surface of the semiconductor layer 402(see process 304 and FIG. 14). The semiconductor layer 402 can be madeof a second semiconductor material (e.g., silicon germanium), which isdifferent from the semiconductor substrate 401 and which is, morespecifically, different from the first semiconductor material 404discussed in greater detail below at process 306. This semiconductorlayer 402 can be formed, for example, by epitaxial deposition or anyother suitable deposition technique. Optionally, this semiconductorlayer 402 can be in-situ doped (or subsequently implanted) so as to havea first-type conductivity at a relatively high conductivity level. Thestack 403 of additional semiconductor layers can be made of alternatinglayers of the first semiconductor material 404 (e.g., silicon) and thesecond semiconductor material 405, which can be formed by epitaxialdeposition or any other suitable deposition technique.

A multi-layer semiconductor fin 410 can be formed from the stack 403 ofadditional semiconductor layers above the semiconductor layer 402 (seeprocess 306 and FIGS. 15A-15B). Techniques for forming a semiconductorfin including, but not limited to, conventional lithographic patterningand etch techniques and sidewall image transfer (SIT) techniques, arewell known in the art. Thus, the details of such techniques have beenomitted from this specification in order to allow the reader to focus onthe salient aspects of the disclosed methods. During subsequentprocessing, nanowire channel region(s) for the NWFET will be formedusing a first portion 411 (e.g., a center portion) of the multi-layersemiconductor fin 410 and source/drain regions for the NWFET will beformed using second portions 412 (e.g., end portions) on opposing sidesof the first portion 411.

For purposes of this disclosure, a semiconductor fin refers to arelatively thin, tall, elongated semiconductor body. The semiconductorfin can be formed (e.g., patterned) so as to be essentially rectangularin shape. That is, the semiconductor fin can have an essentially uniformwidth and height across the length of the semiconductor fin (e.g., inthe first portion 411 and the second portions 412). Alternatively, thesemiconductor fin could be formed (e.g., patterned) so as to have afirst width in the first portion 411 and a second width, which isgreater than the first width, in the second portions 412.

Optionally, the multi-layer semiconductor fin 410 can be doped (e.g.,prior to patterning or after patterning) so as to have the first-typeconductivity at a relatively low conductivity level and, thus, such thatthe nanowire channel region(s) of the NWFET being formed using thismulti-layer semiconductor fin 410 will have this same conductivity.Alternatively, the multi-layer semiconductor fin 410 can remain undopedsuch that the channel region of the NWFET being formed will also beundoped.

A sacrificial gate structure 420, having a sacrificial gate cap 421 anda gate sidewall spacer 422, can be formed adjacent to the opposing sidesand top surface of the first portion 411 of the multi-layersemiconductor fin 410 (see process 308 and FIGS. 15A-15B). Thissacrificial gate structure 420 will function as a placeholder forsubsequent replacement metal gate (RMG) processing (discussed in greaterdetail below at process 320). More specifically, a sacrificial gatestack can be formed over the semiconductor fin. In one exemplaryembodiment, the sacrificial gate stack can include multiple dielectriclayers including at least a blanket dielectric layer and a dielectriccap layer on the blanket dielectric layer. For example, the blanketdielectric layer can be deposited onto the partially completed structure(e.g., over the semiconductor layer 402 and the multi-layersemiconductor fin 410) and polished (e.g., using a chemical mechanicalpolishing (CMP) process) such that it has a thickness that is greaterthan the height of the multi-layer semiconductor fin 410 (i.e., suchthat the top surface of the blanket dielectric layer is above the levelof the top surface semiconductor fin 410). This blanket dielectric layercan be, for example, a blanket layer of silicon nitride, siliconoxycarbide, silicon carbon nitride, silicon boron carbon, or some otherdielectric material that can be selectively etch away from themulti-layer semiconductor fin 410 and semiconductor layer 402 at process320 below. The dielectric cap layer can be deposited onto the blanketdielectric layer. The dielectric cap layer can be, for example, a thinlayer of silicon nitride or some other suitable dielectric material.Lithographic patterning and etch processes can then be performed inorder to form, from this sacrificial gate stack, a sacrificial gatestructure 420 having a sacrificial gate cap 421 (as illustrated). A gatesidewall spacer 422 can further be formed on the sidewalls of thesacrificial gate structure 420, as illustrated in FIGS. 15A-15B. To formthe gate sidewall spacer 422, a relatively thin conformal dielectricspacer layer can be deposited over the partially completed structure. Ananisotropic etch process can then be performed so as to remove theconformal dielectric spacer layer from horizontal surfaces, therebyforming the gate sidewall spacer 422 on the essentially verticalsurfaces of the sacrificial gate structure 420. It should be noted thatthe dielectric material of the dielectric spacer layer should be adifferent dielectric material than that used for the sacrificial gatestructure 420 so that when the sacrificial gate structure 420 isselectively etch away from the multi-layer semiconductor fin 410 andsemiconductor layer 402 at process 320 below, the gate sidewall spacer422 remains intact. For example, if the sacrificial gate structure 420is a silicon nitride structure, then the dielectric spacer layer usedfor the gate sidewall spacer 422 could be a relatively thin conformalsilicon oxycarbide spacer layer.

At least one interlayer dielectric (ILD) layer 430 can subsequently beformed on the semiconductor layer 402 (see process 310 and FIGS.17A-17B). For example, a blanket layer of ILD material can subsequentlybe deposited onto the semiconductor layer 402, over the multi-layersemiconductor fin 410, over the gate sidewall spacer 422 and furtherover the sacrificial gate cap 421 on the sacrificial gate structure 420.This blanket layer of ILD material can be polished (e.g., using a CMPprocess) and then recessed to expose the top surfaces of the secondportions 412 of the multi-layer semiconductor fin 410. Thus, theresulting ILD layer 430 will be positioned laterally adjacent tosidewalls of the multi-layer semiconductor fin 410 and, particularly,adjacent to the sidewalls of the second portions 412 of the multi-layersemiconductor fin 410. The ILD material of this ILD layer 430 should bedifferent from the dielectric materials used for the gate sidewallspacer 422 and for the sacrificial gate structure 420 to allow forrecessing the ILD layer 430 without recessing the gate sidewall spacer422. For example, the ILD material can be silicon dioxide or some othersuitable ILD material (e.g., borophosphosilicate glass (BPSG),tetraethyl orthosilicate (TEOS), fluorinated tetraethyl orthosilicate(FTEOS), etc.).

Recesses 432 can then be formed such that they extend completely throughthe second portions 412 of the multi-layer semiconductor fin 410 to thetop surface of the semiconductor layer 402 below or, alternatively,completely through the second portions 412 of the semiconductor fin 210and further partially into the semiconductor layer 402 below (seeprocess 312). Specifically, to form the recesses 432, an anisotropicetch process that is selective for the semiconductor material of themulti-layer semiconductor fin 410 over the adjacent dielectric materials(e.g., over dielectric materials of the ILD layer 430, the gate sidewallspacer 422 and the sacrificial gate cap 421) can be performed. This etchprocess can stop at the top surface of the semiconductor layer 402, asshown in FIGS. 18A-18C. Alternatively, this etch process can stop whenthe bottoms of the recesses 432 are some distance below the top surfaceof the semiconductor layer 402, but still above the bottom surface ofthe semiconductor layer 402 (see FIGS. 19A-19C).

After the recesses 432 are formed, an oxidation process can be performedin order to form oxide layers on exposed semiconductor surfaces withinthe recesses 432 (i.e., on exposed semiconductor surfaces of thesemiconductor layer 402 at the bottoms of the recesses 432 and exposedsemiconductor surfaces of the different layers of the multi-layersemiconductor fin 410 on the inner sides of the recesses closest to thesacrificial gate structure 420) (see process 314 and FIGS. 20A-20C orFIGS. 21A-21C). Since the semiconductor materials at the exposedsurfaces vary, so will the oxide materials. Specifically, the oxidationprocess will result in alternating layers of a first oxide material 441(e.g., silicon dioxide) and a second oxide material 442 that isdifferent from the first oxide material 441 (e.g., silicon germaniumoxide) being formed on the exposed surfaces of the alternating layers ofthe first semiconductor material 404 and the second semiconductormaterial 405 of the multi-layer semiconductor fin 410 at the inner sidesof the recesses 432. This same oxidation process will also result inlayers of the second oxide material 442 (e.g., silicon germanium oxide)being formed on the exposed second semiconductor material surfaces ofthe semiconductor layer 402 at the bottom of the recesses. It should benoted that if the recesses 432 only extend to the top surface of thesemiconductor layer 402, as shown in FIGS. 18A-18C, without furtherextending into the semiconductor layer 402, then the second oxidematerial 442 will be formed on horizontal surfaces of the semiconductorlayer 402, as shown in FIGS. 20A-20C. However, if the recesses 432extend partially into the semiconductor layer 402 (as shown in FIGS.19A-19C), then the second oxide material will be formed at process 314on vertical and horizontal surfaces of the semiconductor layer 402within lower portions of the recesses 432 (as shown in FIGS. 21A-21C).

For illustration purposes, the remaining processes of the flow diagramof FIG. 13 are illustrated in the drawings with respect to the partiallycompleted structure shown in FIGS. 21A-21C. It should be understood thatthe drawings are not intended to be limiting and that, alternatively,these same processes could, alternatively, be performed with respect tothe partially completed structure shown in FIGS. 20A-20C.

Next, the first oxide material 441 can be selectively removed from thevertical surfaces of the first semiconductor material layers 404 of themulti-layer semiconductor fin 410 on the inner sides of the recesses 432closest to the sacrificial gate structure 420, leaving intact any oxidelayers made of the second oxide material 442 on the bottoms of therecesses 432 as well as on the vertical surfaces of the secondsemiconductor material layers 405 of the multi-layer semiconductor fin410 on the inner sides of the recesses 432 closest to the sacrificialgate structure 420 (see process 316 and FIGS. 22A-22C). For example, aselective isotropic etch process can be performed in order toselectively remove the first oxide material 441 (e.g., silicon dioxide)from within the recesses 432 such that the second oxide material 442remains essentially intact. One exemplary selective isotropic etchprocess that could be used at process 316 to selectively etch silicondioxide over silicon germanium oxide (i.e., to etch silicon dioxide at asignificantly faster rate than silicon germanium oxide) is a remoteplasma-based ammonium fluoride (NH4F) etch process, such as a SiConi™process. Alternatively, any other suitable isotropic etch process whichetches silicon dioxide at a significantly faster rate than silicongermanium oxide could be used. It should be noted that if the ILD layer430 is a silicon dioxide layer, then the layer will also be etched backto some degree at process 316 (not shown).

Following removal of the first oxide material 441 at process 316,source/drain regions 413 can be formed in the recesses 432 and thesecond oxide material 442, which remains intact at the bottoms of therecesses 432, will electrically isolate and physically separate thesource/drain regions 413 from the semiconductor layer 402 below (seeprocess 318 and FIGS. 23A-23C). For example, the source/drain regions413 can be formed by lateral epitaxial deposition of a thirdsemiconductor material on the exposed vertical surfaces of themulti-layer semiconductor fin 410 within the recesses 432 (i.e., on theinner sides of the recesses 432 closest to the sacrificial gatestructure 420). This third semiconductor material of the source/drainregions 413 and the first semiconductor material of the remainingportion 411 of the multi-layer semiconductor fin 410 between thesource/drain regions 413 can be the same material (e.g., silicon).Alternatively, the third semiconductor material can be different fromthe first semiconductor material and can be preselected to enhancecharge carrier mobility, depending upon the conductivity-type of theFINFET being formed. For example, for a P-type FET, the thirdsemiconductor material of the source/drain regions 413 could be silicongermanium (SiGe), which will enhance hole mobility within the P-typeFET's channel region and, thereby enhance performance. For an N-typeFET, the third semiconductor material of the source/drain regions 413could be silicon carbide (SiC), which will enhance electron mobilitywithin the N-type FET's channel region and, thereby enhance performance.

In any case, the source/drain regions 413 can be in-situ doped (orsubsequently implanted) so as to have a second-type conductivity at arelatively high level. This second-type conductivity can be differentfrom the first-type conductivity of the remaining portion 411 of the finthat will be used to form nanowire channel region(s) and thesemiconductor layer 402 below. Specifically, those skilled in the artwill recognize that, for a P-type FET, the first-type conductivity ofthe channel region(s) can be N-type conductivity and the second-typeconductivity of the source/drain regions 413 can be P-type conductivity.In this case, the semiconductor layer 402 below the source/drain regions413 can, optionally, also be doped so as to have the N-typeconductivity, thereby creating diode junctions to further provideprotection against any through-substrate and, particularly, sub-channelregion source-to-drain leakage (i.e., source-to-drain leakage below thenanowire(s)). Contrarily, for an N-type FET, the first-type conductivityof the channel region(s) can be P-type conductivity and the second-typeconductivity of the source/drain regions 413 can be N-type conductivity.In this case, the semiconductor layer 402 below the source/drain regions413 can, optionally, also be doped so as to have the P-typeconductivity, thereby creating diode junctions to further provideprotection against any through-substrate and, particularly, sub-channelregion source-to-drain leakage (i.e., source-to-drain leakage below thenanowire(s)).

Additional processing can subsequently be performed in order to completethe NWFET structure 400 (see process 320 and FIGS. 24A-27C). Thisadditional processing can include, for example, deposition of at leastone additional ILD layer 435 (e.g., made of the same ILD material as theILD layer 430 or a different material). The additional ILD layer 435 canbe polished (e.g., using a CMP process) such that a top surface of thesacrificial gate structure 420 is exposed (see FIGS. 24A-24C). Thesacrificial gate structure 420 can then be selectively removed, therebycreating a gate opening 429 (see process 322 and FIGS. 25A-25C).Creation of the gate opening 429 exposes the top surface and opposingsidewalls of the first portion 411 of the multi-layer semiconductor fin410.

Next, exposed sections of either the second semiconductor material 405or the first semiconductor material 404 can be selectively removed fromwithin the first portion 411, thereby forming one or more nanowires 411a-c or 411′a-b, respectively (see process 324 and FIGS. 26A-26C or FIGS.27A-27C).

Specifically, at process 324 a selective isotropic etch process can beperformed that is selective for the second semiconductor material overthe first semiconductor material. For example, if the firstsemiconductor material 404 is silicon and the second semiconductormaterial 405 is silicon germanium, the silicon germanium can beselectively etched using any of the following exemplary processes: athermal etch process (e.g., using gaseous hydrochloric acid (HCl)), adry plasma etch process, or wet etch process with process specificationsdesigned to ensure the selective etch of silicon germanium over siliconand silicon nitride. Alternatively, any other suitable isotropicselective etch process that selectively etches silicon germanium oversilicon could be used. As a result, as illustrated in FIGS. 26A-26C,only sections of the first semiconductor material 404 that extendlaterally between the source/drain regions 413 will remain in the firstportion 411 and these remaining sections of the first semiconductormaterial 404 effectively form nanowires or, more particularly, nanowirechannel regions 411 a-c (e.g., silicon nanowire channel regions). Asmentioned above, the semiconductor layer 402 is similarly made of thesecond semiconductor material such that this selective isotropic etchprocess 324 will also etch out the semiconductor layer 402 below thefirst portion 411 of the semiconductor body, thereby exposing the bottomsurface of the lowest nanowire channel region 411 a. Depending upon theetch time required to expose the bottom surface of the lowest nanowirechannel region 411 a, the recess formed in the semiconductor layer 402may extend only partially into the semiconductor layer 402 (as shown) ormay extend completely through the semiconductor layer 402 to the topsurface of the substrate 401.

Alternatively, between the process 316 of removing the first oxidematerial and the 318 of forming source/drain regions 413, as discussedin detail above, segments of the second oxide material 442 adjacent tothe semiconductor layer 402 can be protected and segments of the secondoxide material 442 positioned laterally adjacent to vertical surfaces ofthe layers of the second semiconductor material 405 in the first portion411 can be selectively removed. Then, at process at process 324, aselective isotropic etch process can be performed that is selective forthe first semiconductor material over the second semiconductor material.For example, if the first semiconductor material 404 is silicon and thesecond semiconductor material 405 is silicon germanium, the silicon canbe selectively etched using, for example, a plasma-based dry etchprocess or other suitable etch process that selectively etches siliconover silicon germanium and silicon nitride. As a result, as illustratedin FIGS. 27A-27C, only sections of the second semiconductor material 405that extend laterally between the source/drain regions 413 will remainin the first portion 411 and these remaining sections of the secondsemiconductor material 405 effectively form nanowires or, moreparticularly, silicon germanium nanowire channel regions 411′a-b (e.g.,silicon germanium nanowire channel regions) and the lowest of thesesnanowire channel regions 411′a is physically separated from the topsurface of the semiconductor layer 402.

Subsequently, a replacement metal gate (RMG) 425 having a dielectricgate cap 426 can be formed in the gate opening (see process 326), middleof the line (MOL) processing can be performed (not shown), and back endof the line (BEOL) processing can be performed in order to complete theNWFET structure 400 with nanowires 411 a-c, as shown in FIGS. 28A-28C,or the alternative NWFET structure 400′ with nanowires 411′a-b as shownin FIGS. 29A-29C.

In the above-described method, the following exemplary processes can beused to form the RMG 425 adjacent to the nanowire channel regions 411a-c of the NWFET structure 400 or adjacent to the nanowire channelregions 411′a-b of the NWFET structure 400′.

Additional dielectric sidewall spacers can be formed on verticalsurfaces within the gate opening to ensure that the source/drain regions413 will be electrically isolated from the RMG 425. Specifically, theadditional dielectric sidewall spacers can be formed such that they arepositioned laterally adjacent to vertical surfaces of the gate sidewallspacers 422 and also positioned around the ends of the nanowires andpositioned laterally adjacent to vertical surfaces of the source/drainregions 413. Techniques for forming sidewall spacers are well known inthe art. Thus, the details of these techniques have been omitted fromthe present application in order to allow the reader to focus on thesalient aspect of the disclosed method.

A gate dielectric layer can be conformally deposited so that the exposedsurfaces of the nanowire channel regions 411 a-c, 411′a-b are covered(i.e., so that the gate dielectric layer wraps completely around each ofthe nanowire channel regions 411 a-c, 411′a-b). Those skilled in the artwill recognize that, due to the conformal deposition process, the gatedielectric layer may also cover other exposed surfaces within the gateopening (e.g., exposed surfaces of additional dielectric sidewallspacers, of the semiconductor layer 402, of the substrate 401 (ifapplicable), and of the gate sidewall spacers 422). The gate dielectriclayer can be, for example, high-K gate dielectric layer.

Subsequently, a work function metal layer can be conformally depositedin the gate opening so as to cover the gate dielectric layer on eachnanowire channel region. The metal material or metal alloy material ofthe conformal work function metal layer can be preselected in order toachieve the optimal gate conductor work function given the conductivitytype of the NWFET 400 of FIGS. 28A-28C or the NWFET 400′ of FIGS.29A-29C being formed. The work function metal layer can then,optionally, be chamfered. The chamfering process can include: depositinga protective fill material onto the work function metal layer; recessingthe protective fill material; etching away the exposed work functionmetal material from above the protective fill material such that themaximum height of the work function metal layer is below the level ofthe top surface of the gate sidewall spacer; and removing the protectivefill material.

A conductive fill material can be deposited to fill any remaining spacein the gate opening and a polishing process (e.g., a CMP process) can beperformed to remove any RMG materials from above the top surface of theadditional ILD layer 435. A dielectric gate cap 426 can then be formedon the top surfaces of the RMG 425. For example, the conductive fillmaterial can be recessed (i.e., etched back) and a dielectric cap layer(e.g., a silicon nitride cap layer) can be deposited over the partiallycompleted structure so as to fill the recess above the conductive fillmaterial. Next, a polishing process (e.g., a CMP process) can beperformed so as to remove any of the dielectric cap material from abovethe top surface of the additional ILD layer 435, thereby forming thedielectric gate cap 426.

Since various RMG structures and the methods of making them are wellknown in the art and could be incorporated into the NWFET structures 400or 400′ being formed, only the RMG 425, as a whole, is illustrated inFIGS. 28A-28C and FIGS. 29A-29C. The individual components of the RMG425, including the additional dielectric sidewall spacers, the gatedielectric layer, the work function metal layer, the conductive fillmaterial, etc., are not specifically illustrated in the figures in orderto allow the reader to focus on the salient aspects of the disclosedmethod.

For purposes of illustration, the stack 403 of alternating layers of thefirst semiconductor material 404 and the second semiconductor material405 shown in FIG. 14 includes a total of 5 layers. The resulting NWFET400 shown in FIGS. 28A-28C includes three horizontal, stacked, nanowirechannel regions 411 a-c made of the first semiconductor material (e.g.,silicon). The resulting NWFET 400′ shown in FIGS. 28A-28C includes twohorizontal, stacked, nanowire channel regions 411′a-b made of the secondsemiconductor material (e.g., silicon germanium). It should, however, beunderstood that the description and figures are not intended to belimiting. Alternatively, the stack could include a lesser number ofalternating layers of the first semiconductor material 404 and thesecond semiconductor material 405 such that resulting NWFET has a lessernumber (e.g., 1 or 2) of nanowire channel regions. Alternatively, thestack 403 could include a greater number (e.g., 4 or more) ofalternating layers of the first semiconductor material 404 and thesecond semiconductor material 405 such that resulting NWFET has agreater number of nanowire channel regions.

Also disclosed herein are semiconductor structures formed according tothe above-described methods (e.g., see the semiconductor structure shownin FIGS. 12A-12C and the semiconductor structures 400 and 400′ shown inFIGS. 28A-28C and 29A-29C, respectively).

These semiconductor structures 200, 400, 400′ can include a bulksemiconductor substrate 201, 401. This bulk semiconductor substrate 201,401 can, for example, be made of a semiconductor material. Thesemiconductor material of the substrate 201, 401 can be the same as thefirst semiconductor material (e.g., silicon) described below.Alternatively, the semiconductor material can be any other suitablesemiconductor material.

These semiconductor structures 200, 400, 400′ can further includesemiconductor layer 202, 402 on the bulk semiconductor substrate 201,401. This semiconductor layer 202, 402 can be made of a secondsemiconductor material (e.g., silicon germanium), which is differentdifferent the first semiconductor material and, if the substrate is madeof some other semiconductor material, different from the semiconductormaterial of the substrate. Optionally, this semiconductor layer 202, 402can be doped so as to have a first-type conductivity at a relativelyhigh conductivity level.

These semiconductor structures 200, 400, 400′ can further include anon-planar field effect transistor (FET) on the semiconductor layer 202,402. The non-planar FET can be, for example, a fin-type FET (FINFET)200, as shown in FIGS. 12A-12C, or a nanowire FET (NWFET) 400, as shownin FIGS. 28A-28C, or a NWFET 400′ as shown in FIGS. 29A-29C.

In any case, each FET 200, 400, 400′ can include: source/drain regions213, 413 with a second-type conductivity at a relatively highconductivity level; at least one channel region 211, 411 a-c, 411′a-bextending laterally between the source/drain regions 213, 413 andoptionally having the first-type conductivity at a relatively lowconductivity level; and a replacement metal gate (RMG) 225, 425 adjacentto the channel region(s) 211, 411 a-c, 411′a-b.

Referring to the FINFET 200 of FIGS. 12A-12C, the channel region 211 canbe a single fin-shaped channel region that has a bottom surfaceimmediately adjacent to the semiconductor layer 202 and that extendslaterally between the source/drain regions 213. The RMG 225 can bepositioned adjacent to the top surface and opposing sides of the channelregion 211.

Referring to the NWFET 400 of FIGS. 28A-28C and the NWFET 400′ of FIGS.29A-29C, alternatively, the channel region(s) can be in the form of oneor more nanowires (see the nanowire channel regions 411 a-c in the NWFET400 and nanowire channel regions 411′a-b in the NWFET 400′) that extendlaterally between the source/drain regions 413. As illustrated, multiplenanowire channel regions can be horizontally oriented, aligned one abovethe other and physically separated from each other and from thesemiconductor layer 402. The RMG 425 can wrap fully around each nanowirechannel region 411 a-c, 411′a-b.

The channel region 211 of the FINFET 200 can be made of the firstsemiconductor material (e.g., silicon). The nanowire channel region(s)of the NWFETs can be made of either the first semiconductor material(e.g., silicon) or the second semiconductor material (e.g., silicongermanium). For example, as described in detail above with regard to themethod, the nanowire channel regions 411 a-c of the NWFET structure 400are made of the first semiconductor material (e.g., are silicon nanowirechannel regions) and the nanowire channel regions 411′a-b of the NWFET400′ are made of the second semiconductor material (e.g., are silicongermanium nanowire channel regions).

The source/drain regions 213, 413 can be made of a third semiconductormaterial. This third semiconductor material of the source/drain regions213, 413 can be the same as the first semiconductor material (e.g.,silicon). Alternatively, the third semiconductor material can bedifferent from the first semiconductor material and can be preselectedto enhance charge carrier mobility, depending upon the conductivity-typeof the FET. For example, for a P-type FET, the third semiconductormaterial of the source/drain regions 213, 413 could be silicon germanium(SiGe), which will enhance hole mobility within the P-type FET's channelregion and, thereby enhance performance. For an N-type FET, the thirdsemiconductor material of the source/drain regions 213, 413 could besilicon carbide (SiC), which will enhance electron mobility within theN-type FET's channel region and, thereby enhance performance.

In the NWFETs 400, 400′, the RMG 425 can include additional dielectricsidewall spacers on vertical surfaces within the gate opening and,particularly, positioned laterally adjacent to vertical surfaces of thegate sidewall spacers 422 and also positioned around the ends of thenanowires and positioned laterally adjacent to vertical surfaces of thesource/drain regions 413 in order to ensure that the source/drainregions 413 are electrically isolated from the RMG 425.

In the FINFET 200 and in the NWFETs 400, 400′, the RMG 225, 425 canfurther include a conformal gate dielectric layer immediately adjacentto the channel region(s) 211, 411 a-c, 411′a-b. The gate dielectriclayer can be, for example, high-K gate dielectric layer. The RMG 225,425 can further include a conformal work function metal layer on thegate dielectric layer. The metal material or metal alloy material of theconformal work function metal layer can be preselected in order toachieve the optimal gate conductor work function given the conductivitytype of the FET 200, 400, 400′. The RMG 225, 425 can further includeconductive fill material on the work function metal layer. A dielectricgate cap 226, 426 (e.g., a silicon nitride gate cap) can be above thetop surface of the conductive fill material.

It should be noted that, since various RMG structures and the methods ofmaking them are well known in the art and could be incorporated intoFETs 200, 400 and 400′, only the RMG 225, as a whole, is illustrated inthe FIGS. 12A-12C and only the RMG 425, as a whole, is illustrated inFIGS. 28A-28C and FIGS. 29A-29C. The individual components of the RMGs225 and 425, including any additional dielectric sidewall spacers, thegate dielectric layer, the work function metal layer, the conductivefill material, etc., are not specifically illustrated in the figures inorder to allow the reader to focus on the salient aspects of thedisclosed structures.

Additionally, each FET 200, 400, 400′ can include layers of oxidematerial 242, 442 (e.g., layers of silicon germanium oxide), whichelectrically isolate and physically separate the source/drain regions213, 413 from the semiconductor layer 202, 402 below. Thus, these layersof oxide material 242, 442 function as local isolation layers thatminimize and preferably prevent through-substrate and, particularly,sub-channel region source-to-drain leakage. These layers of oxidematerial 242, 442 can be immediately adjacent to the top surface of thesemiconductor layer 202, 402 (e.g., see the partially completedstructures shown in FIGS. 8A-8C and 20A-20C) and the source/drainregions 213, 413 can, in their entirely, be above the top surface of thesemiconductor layer 202, 402. Alternatively, as illustrated in FIGS.12A-12C, 28A-28C, and 29A-29C, the semiconductor layer 202, 402 can havea top surface and source/drain recesses in the top surface on opposingsides of the RMG 225, 425. In this case, the layers of oxide material242, 442 can line the vertical and horizontal surfaces of thesemiconductor layer 202, 402 within the source/drain recesses and thesource/drain regions 213, 413 can be on the oxide material 242, 442filling the remaining portions of the recesses and further extendingvertically above the top surface of the semiconductor layer 202, 402.

It should be noted that, due to the processing techniques describedabove and used to form the NWFET structure 400, additional layers of theoxide material 442 can be contained within the source/drain regions 413and vertically oriented on the sides closest to the RMG 425. Theseadditional layers of the oxide material 442 can further be alignedvertically, physically separated from each other and positionedlaterally between the source/drain regions 413 and those portions of theRMG 425 that are stacked above and/or below the nanowire channelregion(s) 411 a-c. Thus, these additional layers of the oxide material442 can provide additional isolation between the RMG 425 and thesource/drain regions 413.

In the NWFET structure 400′, such additional layers of oxide materialare removed during processing to ensure that the nanowire channelregions 411′a-b are electrically connected to the source/drain regions413.

In the methods and structures described above the non-planar FET (e.g.,the FINFET 200 of FIGS. 12A-12C, the NWFET 400 of FIGS. 28A-28C and theNWFET 400′ of FIGS. 29A-29C) can be an N-type FET or a P-type FET. Asdiscussed above, for an N-type FET, the channel region can have P-typeconductivity (or can be undoped) and the source/drain regions can haveN-type conductivity; whereas, for a P-type FET, the channel region canhave N-type conductivity (or can be undoped) and the source/drainregions can have P-type conductivity. Those skilled in the art willrecognize that different dopants can be used to achieve the differentconductivity types and that the dopants may vary depending upon thedifferent semiconductor materials used. For example, a silicon-basedsemiconductor material (e.g., silicon, silicon germanium, etc.) havingN-type conductivity is typically doped with an N-type dopant (e.g., aGroup V dopant, such as arsenic (As), phosphorous (P) or antimony (Sb)),whereas a silicon-based semiconductor material having P-typeconductivity is typically doped with a P-type dopant (e.g., a Group IIIdopant, such as boron (B) or indium (In)). Alternatively, a galliumnitride (GaN)-based semiconductor material having P-type conductivity istypically doped with magnesium (Mg), whereas a gallium nitride(GaN)-based semiconductor material having N-type conductivity istypically doped with silicon (Si). Those skilled in the art will alsorecognize that different conductivity levels will depend upon therelative concentration levels of the dopants.

Additionally, in the methods and structures described above thenon-planar FET includes a RMG with a dielectric gate cap (e.g., see RMG225 of FIGS. 12A-12C and RMG 425 of FIGS. 28A-28C and FIGS. 29A-29C). Insuch a RMG, the additional dielectric sidewall spacers can be siliconnitride sidewall spacers, silicon oxynitride sidewall spacers, etc. Thegate dielectric layer can be a silicon dioxide gate dielectric layer.Alternatively and preferably, the gate dielectric layer can be a high-Kgate dielectric layer. The high-K gate dielectric layer can be, forexample, a dielectric material with a dielectric constant that isgreater than the dielectric constant of silicon dioxide (i.e., greaterthan 3.9). Exemplary high-K dielectric materials include, but are notlimited to, hafnium (Hf)-based dielectrics (e.g., hafnium oxide, hafniumsilicon oxide, hafnium silicon oxynitride, hafnium aluminum oxide, etc.)or other suitable high-k dielectrics (e.g., aluminum oxide, tantalumoxide, zirconium oxide, etc.). The work function metal of the RMG caninclude a metal material or metal alloy material that is preselected inorder to achieve the optimal gate conductor work function given theconductivity type of the FET. For example, the optimal gate conductorwork function of an NFET will be, for example, between 3.9 eV and about4.2 eV. Exemplary metals (and metal alloys) having a work functionwithin this range include, but are not limited to, hafnium, zirconium,titanium, tantalum, aluminum, and alloys thereof, such as, hafniumcarbide, zirconium carbide, titanium carbide, tantalum carbide, andaluminum carbide. The optimal gate conductor work function for a PFETwill be, for example, between about 4.9 eV and about 5.2 eV. Exemplarymetals (and metal alloys) having a work function within this rangeinclude, but are not limited to, ruthenium, palladium, platinum, cobalt,and nickel, as well as metal oxides (aluminum carbon oxide, aluminumtitanium carbon oxide, etc.) and metal nitrides (e.g., titanium nitride,titanium silicon nitride, tantalum silicon nitride, titanium aluminumnitride, tantalum aluminum nitride, etc.). The conductive fill materialof the RMG can be a blanket layer of a metal or a metal alloy, such astungsten, a tungsten alloy (e.g., tungsten silicide or titaniumtungsten), cobalt, aluminum or any other suitable metal or metal alloy.

It should be understood that the terminology used herein is for thepurpose of describing the disclosed structures and methods and is notintended to be limiting. For example, as used herein, the singular forms“a”, “an” and “the” are intended to include the plural forms as well,unless the context clearly indicates otherwise. Additionally, as usedherein, the terms “comprises” “comprising”, “includes” and/or“including” specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Furthermore, asused herein, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., are intended todescribe relative locations as they are oriented and illustrated in thedrawings (unless otherwise indicated) and terms such as “touching”, “indirect contact”, “abutting”, “directly adjacent to”, “immediatelyadjacent to”, etc., are intended to indicate that at least one elementphysically contacts another element (without other elements separatingthe described elements). The term “laterally” is used herein to describethe relative locations of elements and, more particularly, to indicatethat an element is positioned to the side of another element as opposedto above or below the other element, as those elements are oriented andillustrated in the drawings. For example, an element that is positionedlaterally adjacent to another element will be beside the other element,an element that is positioned laterally immediately adjacent to anotherelement will be directly beside the other element, and an element thatlaterally surrounds another element will be adjacent to and border theouter sidewalls of the other element. The corresponding structures,materials, acts, and equivalents of all means or step plus functionelements in the claims below are intended to include any structure,material, or act for performing the function in combination with otherclaimed elements as specifically claimed.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method of forming a semiconductor structure,the method comprising: forming a gate structure adjacent to a firstportion of a semiconductor fin, the semiconductor fin comprising a firstsemiconductor material and being on a semiconductor layer comprising asecond semiconductor material that is different from the firstsemiconductor material, and the first portion being positioned laterallybetween second portions; forming a dielectric layer on the semiconductorlayer and positioned laterally adjacent to sidewalls of thesemiconductor fin; forming recesses through the second portions toexpose the semiconductor layer; performing an oxidation process to formoxide layers on exposed semiconductor surfaces, the oxide layerscomprising a first oxide material of the first semiconductor materialand a second oxide material that is different from the first oxidematerial of the second semiconductor material; selectively removing thefirst oxide material; and forming source/drain regions in the recesses,wherein the second oxide material electrically isolates and physicallyseparates the source/drain regions from the semiconductor layer.
 2. Themethod of claim 1, wherein the first portion comprises a channel regionand wherein the second oxide material that remains on the semiconductorlayer after the selectively removing of the first oxide material reducessource-to-drain leakage below the channel region.
 3. The method of claim1, further comprising: providing a semiconductor substrate, thesemiconductor substrate comprising the first semiconductor material;forming the semiconductor layer on the semiconductor substrate; andforming the semiconductor fin on the semiconductor layer, wherein thefirst semiconductor material comprises silicon such that, following theoxidation process, the first oxide material comprises silicon oxide, andwherein the second semiconductor material comprises silicon germaniumsuch that, following the oxidation process, the second oxide materialcomprises silicon germanium oxide.
 4. The method of claim 1, wherein theforming of the source/drain regions comprises performing a lateralepitaxial deposition process to grow a third semiconductor material onexposed vertical surfaces of the semiconductor fin within the recesses.5. The method of claim 4, the third semiconductor material and the firstsemiconductor material comprising a same semiconductor material.
 6. Themethod of claim 4, the third semiconductor material and the firstsemiconductor material comprising different semiconductor materials. 7.The method of claim 1, wherein the forming of the recesses comprisesetching the recesses such that the recesses extend vertically throughthe second portions to expose only a top surface of the semiconductorlayer, wherein, following the oxidation process, the second oxidematerial is on the top surface only of the semiconductor layer, andwherein, following the forming of the source/drain regions, thesource/drain regions are entirely above the top surface of thesemiconductor layer.
 8. The method of claim 1, wherein the forming ofthe recesses comprises etching the recesses such that the recessesextend vertically through the second portions and into the semiconductorlayer, and wherein, following the oxidation process, the second oxidematerial is on vertical and horizontal surfaces of the semiconductorlayer within lower portions of the recesses.
 9. A method of forming asemiconductor structure, the method comprising: forming a gate structureadjacent to a first portion of a semiconductor fin, the semiconductorfin comprising a first semiconductor material and being on asemiconductor layer comprising a second semiconductor material that isdifferent from the first semiconductor material, and the first portionbeing positioned laterally between second portions; forming a dielectriclayer on the semiconductor layer and positioned laterally adjacent tosidewalls of the semiconductor fin; forming recesses through the secondportions to expose the semiconductor layer; performing an oxidationprocess to form oxide layers on exposed semiconductor surfaces, theoxide layers comprising a first oxide material of the firstsemiconductor material and a second oxide material that is differentfrom the first oxide material of the second semiconductor material;selectively removing the first oxide material; and forming source/drainregions in the recesses, wherein remaining oxide layers of the secondoxide material after the selectively removing of the first oxidematerial have bottom surfaces immediately adjacent to the semiconductorlayer and top surfaces opposite the bottom surfaces and immediatelyadjacent to the source/drain region so that the second oxide materialelectrically isolates and physically separates the source/drain regionsfrom the semiconductor layer.
 10. The method of claim 9, wherein thefirst portion comprises a channel region and wherein the second oxidematerial that remains on the semiconductor layer after the selectivelyremoving of the first oxide material reduces source-to-drain leakagebelow the channel region.
 11. The method of claim 9, further comprising:providing a semiconductor substrate, the semiconductor substratecomprising the first semiconductor material; forming the semiconductorlayer on the semiconductor substrate; and forming the semiconductor finon the semiconductor layer, wherein the first semiconductor materialcomprises silicon such that, following the oxidation process, the firstoxide material comprises silicon oxide, and wherein the secondsemiconductor material comprises silicon germanium such that, followingthe oxidation process, the second oxide material comprises silicongermanium oxide.
 12. The method of claim 9, wherein the forming of thesource/drain regions comprises performing a lateral epitaxial depositionprocess to grow a third semiconductor material on exposed verticalsurfaces of the semiconductor fin within the recesses and wherein thethird semiconductor material and the first semiconductor materialcomprise a same semiconductor material.
 13. The method of claim 9,wherein the forming of the source/drain regions comprises performing alateral epitaxial deposition process to grow a third semiconductormaterial on exposed vertical surfaces of the semiconductor fin withinthe recesses and wherein the third semiconductor material and the firstsemiconductor material comprise different semiconductor materials. 14.The method of claim 9, wherein the forming of the recesses comprisesetching the recesses such that the recesses extend vertically throughthe second portions to expose only a top surface of the semiconductorlayer, wherein, following the oxidation process, the second oxidematerial is on the top surface only of the semiconductor layer, andwherein, following the forming of the source/drain regions, thesource/drain regions are entirely above the top surface of thesemiconductor layer.
 15. The method of claim 9, wherein the forming ofthe recesses comprises etching the recesses such that the recessesextend vertically through the second portions and into the semiconductorlayer, and wherein, following the oxidation process, the second oxidematerial is on vertical and horizontal surfaces of the semiconductorlayer within lower portions of the recesses.